The present invention relates, in particular, to an antenna device to be attached to a body of an automobile for receiving, for example, AM, FM, or TV broadcasting or wireless telephone, etc. and to a communication system using such an antenna device.
With the advance of the car multimedia era, in addition to an AM/FM radio, various radio equipments such as a TV receiver, a wireless telephone set, and a navigation system have been recently installed in the automobile. Also hereafter, information and services may be increasingly provided through radio wave and the importance of an antenna will grow accordingly.
Generally, in the wireless telephone set or any other communication devices which are used for mobile communication and are capable of transmitting and receiving, the antenna is used for both transmitting and receiving and a single terminal connected to that antenna performs a double function of an input terminal for the receiving section and an output terminal for the transmitting section through a common component such as a divider, a mixer, a circulator, or a switch or the like. During the receiving operation, such a common component prevents a received signal from entering the transmitting section through the antenna and allows it to enter the receiving section properly. On the contrary, during the transmitting operation, that component prevents a transmission signal from entering the receiving section from the transmitting section and allows it to be emitted through the antenna.
As described above, however, when an antenna is used for both transmitting and receiving with a common component in a communication device, it may generally require a high costcommon component and the communication device itself may become very expensive. In addition, there is a problem that the reception sensitivity may be degraded with an increased transmission loss by using a single antenna with a common component.
Moreover, since a receiving amplifier and a transmitting amplifier are certainly installed at the side of the communication device, there is a problem that a cable connecting between the antenna and the communication device may degrade the reception level and the transmission power.
In view of these problems of conventional antennas, the present invention aims to provide an antenna device and a communication system which can improve the reception sensitivity with a reduced transmission loss and which can be implemented at a lower cost.
Also, the present invention aims to provide an antenna device which can further improve its gain.
In addition, the present invention aims to provide a digital television broadcasting receiving device and a receiving method which can reduce reception disturbance during the mobile reception of digital data.
A 1st invention of the present invention (corresponding to claim 1) is an antenna device comprising:
a conductive earth substrate;
a receiving element located in the proximity of said conductive earth substrate and having a receiving terminal; and
a transmitting element located in the proximity of said receiving element and having a transmitting terminal,
characterized in that an end of said receiving element and an end of said transmitting element are connected to said conductive earth substrate for grounding through a common portion and the frequency band of said receiving element is different from that of said transmitting element.
A 2nd invention of the present invention (corresponding to claim 2) is an antenna device comprising:
a conductive earth substrate;
a receiving element located in the proximity of said conductive earth substrate and having a receiving terminal; and
a transmitting element located in the proximity of said receiving element and having a transmitting terminal,
characterized in that an end of said receiving element and an end of said transmitting element are connected to said conductive earth substrate for grounding at separate locations and the frequency band of said receiving element is different from that of said transmitting element.
A 3rd invention of the present invention( corresponding to claim 12) is an antenna device comprising:
a conductive earth substrate;
an antenna element having an end connected to said conductive earth substrate for grounding and formed on a common circuit board; and
a feeding terminal pulled out of said antenna element,
characterized in that a resonant circuit is inserted between said feeding terminal and the other end of said antenna element which is not grounded.
A 4th invention of the present invention (corresponding to claim 18) is a communication system comprising:
an antenna device having a conductive earth substrate, an antenna element formed on a common circuit board located in the proximity of said conductive earth substrate, and a receiving amplifier provided on said common circuit board between said antenna element and a feeding terminal;
a receiver having a power supply section to supply electric power to said receiving amplifier of said antenna device; and
a feeding line for connecting said feeding terminal of said antenna device to a signal input section of said receiver,
characterized in that a direct-current blocking capacitor is provided between said receiving amplifier of said antenna device and said feeding terminal and at the input terminal of a receiving amplifier of said receiver, respectively, and electric power is supplied by said power supply section to said receiving amplifier of said antenna device through said feeding line.
A 5th invention of the present invention (corresponding to claim 20) is a communication system comprising:
an antenna device of the present invention (corresponding to claim 15);
a receiver having a receiving channel setting circuit which generates a bias voltage for said voltage-variable capacitor element of said antenna device; and
a feeding line for connecting a signal input section of said receiver to a feeding terminal of said antenna device,
characterized in that said voltage-variable capacitor element of said antenna device is connected to said feeding terminal, a direct-current blocking capacitor is provided between said antenna element and said feeding terminal and at the input terminal of a receiving amplifier of said receiver, respectively, and a receiving channel is established by varying the bias voltage generated by said receiving channel setting circuit.
A 6th invention of the present invention (corresponding to claim 21) is a communication system comprising:
an antenna device of the present invention (corresponding to any one of claims 1 through 10);
a communication device having a receiving amplifier and a transmitting amplifier;
a receiving connection line for connecting the receiving terminal of said antenna device to said receiving amplifier of said communication device; and
a transmitting connection line for connecting the transmitting terminal of said antenna device to said transmitting amplifier of said communication device.
A 7th invention of the present invention (corresponding to claim 22) is a communication system comprising:
an antenna device having a conductive earth substrate, a receiving element having a receiving terminal formed on a common circuit board located in the proximity of said conductive earth substrate, a transmitting element having a transmitting terminal formed on said common circuit board located in the proximity of said receiving element, and a transmitting/receiving changeover circuit provided on said common circuit board and capable of switching said receiving terminal and said transmitting terminal;
a feeding line connected to said transmitting/receiving changeover circuit; and
a communication device connected to said feeding line and capable of both transmitting and receiving, characterized in that said transmitting/receiving changeover circuit of said antenna device is controlled by using a switch signal to change over to the transmission operation in said communication device.
A 8th invention of the present invention (corresponding to claim 23) is a communication system comprising:
an antenna device of the present invention (corresponding to claim 11);
a communication device having a power supply section to supply electric power to said receiving amplifier of said antenna device and capable of both transmitting and receiving; and
a feeding line for connecting a common terminal of said antenna device to a signal input/output section of said communication device, characterized in that a direct-current blocking capacitor is provided between a common component of said antenna element and said common terminal and at the input/output terminal of said communication device, respectively, and electric power is supplied by said power supply section to a receiving amplifier of said antenna device through said feeding line.
A 9th invention of the present invention (corresponding to claim 30) is an antenna device comprising:
a conductive earth substrate;
a main antenna element connected to said conductive earth substrate through a first ground connection to be substantially parallel to said conductive earth substrate; and
a passive element connected to said conductive earth substrate through a second ground connection along said main antenna element.
A 10th invention of the present invention (corresponding to claim 38) is a digital television broadcasting receiving device comprising:
input means which is an antenna device of the present invention (corresponding to any one of claims 1 through 37) and converts electromagnetic waves into electric signals;
delay means for receiving a signal from said input means and delaying it;
synthesis means for synthesizing a signal from said delay means and a signal from said input means;
reception means for performing frequency conversion on a signal from said synthesis means; and
demodulation means for converting a signal from said reception means into a baseband signal, characterized in that the delay time used in said delay means and the synthesis ratio used in said synthesis means can be established arbitrarily.
A 11th invention of the present invention (corresponding to claim 39) is a digital television broadcasting receiving device comprising:
input means which is an antenna device of the present invention( corresponding to any one of claims 1 through 37) and converts electromagnetic waves into electric signals;
delay means for receiving a signal from said input means and delaying it;
synthesis means for synthesizing a signal from said delay means and a signal from said input means;
reception means for performing frequency conversion on a signal from said synthesis means;
demodulation means for converting a signal from said reception means into a baseband signal;
delayed wave estimation means for receiving a signal indicating the demodulation conditions from said demodulation means and estimating a delayed wave contained in a signal from said input means; and
synthesis control means for controlling said synthesis means and said delay means in accordance with a signal from said delayed wave estimation means, characterized in that either the signal synthesis ratio used in said synthesis means or the delay time used in said delay means can be controlled in accordance with a signal from said synthesis control means.
A 12th invention of the present invention (corresponding to claim 40) is a digital television broadcasting receiving device comprising:
input means which is an antenna device of the present invention (corresponding to any one of claims 1 through 37) and converts electromagnetic waves into electric signals;
reception means for performing frequency conversion on a signal from said input means;
delay means for receiving a signal from said reception means and delaying it;
synthesis means for synthesizing a signal from said delay means and a signal from said reception means; and
demodulation means for converting a signal from said synthesis means into a baseband signal, characterized in that the delay time used in said delay means and the synthesis ratio used in said synthesis means can be established arbitrarily.
A 13th invention of the present invention (corresponding to claim 41) is a digital television broadcasting receiving device comprising:
input means which is an antenna device of the present invention( corresponding to any one of claims 1 through 37) and converts electromagnetic waves into electric signals, a reception means for performing frequency conversion on a signal from said input means;
delay means for receiving a signal from said reception means and delaying it;
synthesis means for synthesizing a signal from said delay means and a signal from said reception means;
demodulation means for converting a signal from said synthesis means into a baseband signal;
delayed wave estimation means for receiving a signal indicating the demodulation conditions from said demodulation means and estimating a delayed wave contained in a signal from said input means; and
synthesis control means for controlling said synthesis means and said delay means in accordance with a signal from said delayed wave estimation means, characterized in that either the signal synthesis ratio used in said synthesis means or the delay time used in said delay means can be controlled in accordance with a signal from said synthesis control means.
A 14th invention of the present invention (corresponding to claim 42) is a digital television broadcasting receiving device comprising:
input means which is an antenna device of the present invention (corresponding to any one of claims 1 through 37) and converts electromagnetic waves into electric signals;
reception means for performing frequency conversion on a signal from said input means;
demodulation means for converting a signal from said reception means into a baseband signal;
delayed wave estimation means for receiving information on the demodulation conditions from said demodulation means and estimating a delayed wave contained in a signal from said input means; and
demodulation control means for controlling said demodulation means based on delayed wave information from said delayed wave estimation means, characterized in that a transfer function to be handled by said demodulation means is controlled based on a control signal from said demodulation control means.